Since you're using a bulky Gyarados set, why don't you opt for Bounce over Earthquake? You're not going to hit anything much with Earthquake, unlike Bounce, which can ruin Fighting-types that run amok in this metagame. Not to mention that chance of paralysis which can generally help your team. I've had experiences where Gyarados swept an entire team with just Bounce. You might be able to experience that too.

Also, on Forretress, why don't you consider using Gyro Ball over Payback? Like Spino said, you wouldn't want to stay in the field especially if your opponent can outspeed and can KO you.